EP3696514B1 - Sensor assembly and method for operating a sensor assembly - Google Patents

Description

TECHNICAL FIELD

The present invention relates to a sensor arrangement for detecting variable physical measured variables and a method for operating such a sensor arrangement.

STATE OF THE ART

For the detection of variable physical measured variables, such as temperature or humidity, sensor arrangements are known which output the corresponding measured variables after suitable preprocessing and further processing via a signal processing unit as pulse-width-modulated signals or PWM signals. The measured variable recorded is contained in the generated PWM signal in a coded manner via the pulse duty factor p of the PWM signal. The pulse duty factor p here is the ratio of the duration t _{H of} a HIGH level to the signal _{period duration t P} = t _H + t _L im to understand rectangular PWM signal, ie p = t _H / t _P ; t _L denotes the duration of a LOW level in the PWM signal. For further processing of the PWM signal, provision is usually made to demodulate and amplify the PWM signal with the duty cycle p, which is dependent on the measured variable, via an amplifier unit and thus convert it into an analog current or voltage signal within a certain current or voltage range; For example, in the case of a current signal, a current range between 4 mA and 20 mA or, in the case of a voltage signal, a voltage range between 0 V and 10 V is usual for the analog output signal. However, both the electronic components used in the signal processing unit and in the amplifier unit are subject to fluctuations in practice, which can result, for example, in variable voltages of the PWM signal, fluctuating offset voltages of operational amplifiers or varying resistance tolerances of amplifier stages. This leads to the fact that, despite identical measured variables, the measured values output by the sensor arrangement in the form of the analog current or voltage signals from sensor arrangement to sensor arrangement fluctuate in an unacceptable manner and thus impair the desired measuring accuracy.

From the US 7,731,417 B2 In order to solve such problems in the case of a temperature measurement, it is known to carry out a temperature measurement at a known reference temperature in a setting mode preceding the measurement operation. Several correction variables are determined and stored in a memory. In the measurement mode, the correction variables are then used to correct the pulse width of the PWM signal as a function of the temperature. In the proposed solution, the PWM signal is generated via analog signal processing components to which the correction variables are supplied from the memory. This requires complex D / A converters in order to convert the stored digital correction variables into suitable analog signals. The higher the requirements for the accuracy of the PWM signal, the greater the requirements for the Resolution of the D / A converter; the circuit complexity increases considerably in the case of a desired higher resolution.

SUMMARY OF THE INVENTION

The present invention is based on the object of creating a sensor arrangement for acquiring variable physical measured variables, which enables a highly accurate and reliable output of analog current or voltage signals with regard to the physical measured variables recorded with the least possible circuitry complexity.

According to the invention, this object is achieved by a sensor arrangement having the features of claim 1.

Furthermore, this invention is based on the object of creating a method for operating a sensor arrangement for acquiring variable physical measured variables, which method enables high-precision output of analog current or voltage signals with regard to the physical measured variables that are recorded.

According to the invention, this object is achieved by a method having the features of claim 9.

Advantageous embodiments of the sensor arrangement according to the invention and the method according to the invention result from the measures that are listed in the respective dependent claims.

• mindestens einen Sensor, der veränderliche physikalische Messgrößen erfasst und ausgangsseitig ein Sensor-Rohsignal bereitstellt,
• eine digitale Signalverarbeitungseinheit zur Vorverarbeitung des vom Sensor bereitgestellten Sensor-Rohsignals in ein Sensor-Signal, wobei die Signalverarbeitungseinheit das Sensor-Signal weiterverarbeitet und dabei in ein pulsweitenmoduliertes Ausgangssignal mit einem von der Messgröße abhängigen Tastverhältnis umsetzt, wozu in einer Speichereinheit mehrere anordnungsspezifische Korrekturparameter abgelegt sind, welche die Signalverarbeitungseinheit zur Umsetzung des Sensor-Signals in das pulsweitenmodulierte Ausgangssignal heranzieht, wobei als anordnungsspezifische Korrekturparameter zumindest ein minimaler Tastverhältnisparameter-Grenzwert und ein maximaler Tastverhältnisparameter-Grenzwert in der Speichereinheit abgelegt ist und - eine Verstärkereinheit, die das pulsweitenmodulierte Ausgangssignal in ein analoges Spannungs- oder Stromsignal umsetzt.

The sensor arrangement according to the invention comprises

• at least one sensor that records changing physical measured variables and provides a raw sensor signal on the output side,
• a digital signal processing unit for preprocessing the raw sensor signal provided by the sensor into a sensor signal, the Signal processing unit processes the sensor signal and converts it into a pulse-width-modulated output signal with a pulse-duty factor dependent on the measured variable, for which purpose a number of configuration-specific correction parameters are stored in a memory unit, which the signal processing unit uses to convert the sensor signal into the pulse-width-modulated output signal, the configuration-specific correction parameters being used at least one minimum pulse duty factor parameter limit value and a maximum pulse duty factor parameter limit value are stored in the memory unit and an amplifier unit which converts the pulse-width-modulated output signal into an analog voltage or current signal.

An arrangement-specific conversion rule is advantageously stored in the digital signal processing unit, which describes a linear relationship between the measured value of the sensor signal and a duty cycle parameter of the pulse-width-modulated output signal.

It is also possible that a minimum sensor limit measured value and a maximum sensor limit measured value are also stored in the memory unit, which limit the sensor measuring range,

in der digitalen Signalverarbeitungseinheit abgelegt sein, mit PWM_OUT_NOW := Tastverhältnisparameter des PWM-Signals MV_NOW := Messwert des Sensors ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$

• d_PWM := PWM_OUT_MIN - MV_OUT_MIN · k_PWM
• PWM_OUT_MAX := maximaler Tastverhältnisparameter-Grenzwert
• PWM_OUT_MIN := minimaler Tastverhältnisparameter-Grenzwert
• MV_OUT_MAX := maximaler Sensor-Grenzmesswert
• MV_OUT_MIN := minimaler Sensor-Grenzmesswert

The relationship $$\mathrm{PWM}\_\mathrm{OUT}\_\mathrm{NOW}=\mathrm{MV}\_\mathrm{NOW}\cdot {\mathrm{k}}_{\mathrm{PWM}}+{\mathrm{d}}_{\mathrm{PWM}}$$

be stored in the digital signal processing unit, with PWM_OUT_NOW: = duty cycle parameter of the PWM signal MV_NOW: = measured value of the sensor ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$

• d _PWM : = PWM_OUT_MIN - MV_OUT_MIN · k _PWM
• PWM_OUT_MAX: = maximum duty cycle parameter limit value
• PWM_OUT_MIN: = minimum duty cycle parameter limit value
• MV_OUT_MAX: = maximum sensor limit measured value
• MV_OUT_MIN: = minimum sensor limit measured value

It can be provided that the at least one sensor, the digital signal processing unit and the memory unit are arranged together in an ASIC and the amplifier unit is embodied separately from the ASIC.

In this case, the memory unit can be designed as a non-volatile memory unit.

In one possible embodiment, the amplifier unit can be designed as an amplifier circuit with a low-pass filter.

Two sensors are advantageously provided, of which a first sensor is designed as a temperature sensor and a second sensor is designed as a humidity sensor.

The method according to the invention is used to operate a sensor arrangement in a measuring operation and in a calibration operation.

• über mindestens einen Sensor eine veränderliche physikalische Messgröße erfasst und ausgangsseitig ein Sensor-Rohsignal bereitgestellt, und
• über eine digitale Signalverarbeitungseinheit das vom Sensor bereitgestellte Sensor-Rohsignal in ein Sensor-Signal vorverarbeitet und das Sensor-Signal in ein pulsweitenmoduliertes Ausgangssignal mit einem von der Messgröße abhängigen Tastverhältnis umgesetzt, und
• über eine Verstärkereinheit das pulsweitenmodulierte Ausgangssignal in ein analoges Spannungs- oder Stromsignal umgesetzt.

This is in measurement mode

• A variable physical measured variable is detected via at least one sensor and a raw sensor signal is provided on the output side, and
• The raw sensor signal provided by the sensor is preprocessed into a sensor signal via a digital signal processing unit and the sensor signal is converted into a pulse-width-modulated output signal with a pulse duty factor that is dependent on the measured variable, and
• The pulse-width-modulated output signal is converted into an analog voltage or current signal via an amplifier unit.

In a calibration operation preceding the measuring operation, several arrangement-specific correction parameters are stored in a memory unit which are used by the signal processing unit in the measuring operation Implementation of the sensor signal into the pulse-width-modulated output signal can be used, with at least one minimum duty cycle parameter limit value and one maximum duty cycle parameter limit value being stored in the memory unit as arrangement-specific correction parameters.

In calibration mode, an arrangement-specific conversion rule is preferably stored in the digital signal processing unit, which describes a linear relationship between the measured value of the sensor signal and a duty cycle parameter of the pulse-width-modulated output signal.

It is also possible for a minimum sensor limit measured value and a maximum sensor limit measured value to be stored in the memory unit, which limit the sensor measuring range.

in der digitalen Signalverarbeitungseinheit abgelegt, mit PWM_OUT_NOW := Tastverhältnisparameter des PWM-Signals MV_NOW := Messwert des Sensor-Signals

• ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$
  
• d_PWM := PWM_OUT_MIN - MV_OUT_MIN · k_PWM
• PWM_OUT_MAX := maximaler Tastverhältnisparameter-Grenzwert
• PWM_OUT_MIN := minimaler Tastverhältnisparameter-Grenzwert
• MV_OUT_MAX := maximaler Sensor-Grenzmesswert
• MV_OUT_MIN := minimaler Sensor-Grenzmesswert

In one possible embodiment, the arrangement-specific conversion rule is the relationship $$\mathrm{PWM}\_\mathrm{OUT}\_\mathrm{NOW}=\mathrm{MV}\_\mathrm{NOW}\cdot {\mathrm{k}}_{\mathrm{PWM}}+{\mathrm{d}}_{\mathrm{PWM}}$$

stored in the digital signal processing unit, with PWM_OUT_NOW: = duty cycle parameter of the PWM signal MV_NOW: = measured value of the sensor signal

• ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$
  
• d _PWM : = PWM_OUT_MIN - MV_OUT_MIN · k _PWM
• PWM_OUT_MAX: = maximum duty cycle parameter limit value
• PWM_OUT_MIN: = minimum duty cycle parameter limit value
• MV_OUT_MAX: = maximum sensor limit measured value
• MV_OUT_MIN: = minimum sensor limit measured value

It is also possible for the calibration operation to be carried out without changing the temperature of the sensor arrangement.

Using the measures according to the invention, it is now possible to ensure a highly precise detection of the respective measured values in the case of an output of analog voltage or current signals. This is also guaranteed when individual components of the corresponding sensor arrangement exhibit manufacturing-related component fluctuations.

Furthermore, the measures according to the invention make it possible to considerably reduce the circuit complexity required to provide the high-precision, output-side analog current or voltage signals. In particular, no complex components such as D / A converters are required due to the digital signal processing provided for generating the PWM signal.

The digital signal processing provided also enables an extremely flexible setting of the relationship between the respective measured variable and the pulse duty factor of the PWM signal.

Further details and advantages of the present invention are explained on the basis of the following description of exemplary embodiments of the sensor arrangement according to the invention and the method according to the invention in conjunction with the figures.

BRIEF DESCRIPTION OF THE DRAWINGS It shows

Figure 1

a highly schematic block diagram of an embodiment of the sensor arrangement according to the invention;

Figure 2a

a schematic detailed representation of part of the block diagram in FIG Figure 1 for exemplary Explanation of the conversion of a PWM signal into an analog voltage signal;

Figure 2b

a further schematic illustration for converting a PWM signal into an analog voltage signal via linear interpolation;

Figure 3

a schematic representation for converting a PWM signal into an analog voltage signal.

DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the sensor arrangement according to the invention for acquiring variable physical measured variables is shown in Figure 1 shown in a highly schematic block diagram.

The sensor arrangement has, on the one hand, an integrated circuit in the form of an ASIC 10, which comprises various analog and digital signal processing components; their functions are described in detail below. The ASIC 10 is designed as a mixed-signal ASIC and is suitable for processing analog and digital signals.

On the other hand, the sensor arrangement according to the invention comprises an amplifier unit 20 which converts a measured variable-dependent PWM signal PWM supplied by ASIC 10 into an analog output signal. In the present exemplary embodiment, conversion into an analog voltage signal U _{OUT is} provided, as is also the case in FIG Figure 3 is shown in more detail. Furthermore it is off Figure 3 It can be seen that the PWM signal has an essentially rectangular profile between a LOW level (0V) and a HIGH level (VDD), the HIGH level corresponding to the supply voltage VDD of the ASIC 10. The analog voltage signal U _OUT generated in this way is then not fed into the Figures shown subsequent electronics output for further processing. In one possible embodiment, the amplifier unit 20 is designed as an amplifier circuit with a low-pass filter; the low pass can be designed as a first or higher order low pass. That is, in addition to filtering and converting the PWM signal PWM, the amplifier unit 20 also amplifies the resulting analog signal U _{OUT in} a suitable manner. In this case, for example, the supply voltage VDD of the ASIC 10 can be amplified from VDD = 3.3V to 10V in the analog voltage signal UOUT.

In the figure, reference numeral 15 denotes an LDO (Low Drop Out) voltage regulator, via which the ASIC 10 is supplied with voltage. The LDO voltage regulator 15 reduces the external supply voltage to a voltage value that is suitable for the ASIC, e.g. 1.8V. In the present example, the sensor arrangement according to the invention outputs an analog voltage signal in the range between 0 V and 10 V to the subsequent electronics.

In the example shown, the recording of the temperature T and the humidity rH is provided as variable physical measured variables. To detect the measured variables T, rH, a first sensor 11 for temperature measurement and a second sensor 12 for humidity measurement are formed in the analog part of ASIC 10. The sensor 11 for temperature measurement can comprise a transistor in which a temperature-dependent base-emitter voltage is measured with the aid of an AD converter and converted into a digital signal. A plate capacitor can be used as sensor 12 for humidity measurement, the humidity-dependent capacitance of which is detected by means of a capacitance measuring stage and converted into a digital signal. The sensors 11, 12 integrated in the ASIC 10 thus provide raw sensor signals T_RAW, rH_RAW with regard to the respective measured variables T, rH on the output side.

The sensor raw signals T_RAW, rH_RAW are digital data words, e.g. in the form of 16-bit data words, which are sent by the sensors 11, 12 are each fed to a downstream digital signal processing unit 13 in ASIC 10. The digital signal processing unit 13 is designed as a digital signal processor in the ASIC 10 and is used, among other things, for preprocessing and further processing of the raw sensor signals T_RAW, rH_RAW into sensor signals T_ASIC, rH_ASIC. As shown in Figure 1 the digital signal processing unit 13 comprises at least two separate functional blocks 13.1, 13.2; It should be pointed out that this representation was chosen only for the following more understandable explanation of the mode of operation of the signal processing in the digital signal processing unit 13 and is not to be understood as restrictive with regard to the design of the digital signal processing unit 13.

In the signal processing unit 13 or in the first function block 13.1 of the same, the raw sensor signals T_RAW, rH_RAW first undergo preprocessing. In this case, for example, a linearization can take place via which any non-linearities of the sensors 11, 12 that may be present can be compensated. Furthermore, errors that are caused by fluctuations in the manufacture of the sensors 11, 12 can be corrected as part of the preprocessing. It is also possible to compensate for temperature cross-sensitivities of the humidity sensor and the self-heating of the ASIC 10, etc. In connection with the preprocessing of the raw sensor signals T_RAW, rH_RAW, it should be noted that the preprocessing can basically take place in a wide variety of ways; these are no measures essential to the invention.

The signals generated in the first function block 13.1 of the digital signal processing unit 13 from the raw sensor signals T_RAW, rH_RAW as part of the preprocessing are referred to below as sensor signals T_ASIC or rH_ASIC. In the second function block 13.2 of the digital signal processing unit 13, the sensor signals T_ASIC, rH_ASIC are then processed further and converted into a pulse-width-modulated output signal PWM, which has a duty cycle p dependent on the respective measured variable T, rH. As already explained above, as Duty cycle p to understand the ratio of the duration t _{H of} a HIGH level (eg 3.3V) to the signal _{period duration t P} = t _H + t _L in the square-wave PWM signal, ie p = t _H / t _P ; t _L denotes the duration of a LOW level (eg 0V) in the PWM signal. With a signal period tp predetermined by a fixed clock frequency, the duration t _{H is} proportional to the value of the measured variable T or rH. In the case of a PWM resolution of 16 bits, the signal period tp can thus be divided into 2 ¹⁶ = 65,536 intervals or steps. This means that values of the measured variable T, rH in the range between 0 (PWM signal consistently at LOW level) and 65,535 (PWM signal almost consistently at HIGH level) can be coded and output via the pulse duty factor p of the PWM signal PWM. The duration t _{H of} the HIGH level is also referred to below as the duty cycle parameter or PWM value. The respective pulse duty factor p is then clearly characterized via the pulse duty factor parameter; the pulse duty factor parameter can assume values in the range between 0 and 65,535 with a resolution of 16 bit.

In order to minimize the problems with component fluctuations discussed at the beginning, it is provided for the sensor arrangement according to the invention that it can be operated in two different modes, namely in a measuring mode and in a calibration mode. In measuring mode, the respective physical measured variables T, rH are recorded, the measured variables are converted into a pulse-width-modulated output signal PWM and then the PWM signal PWM is converted into an analog voltage signal U _OUT suitable for further processing. The calibration operation preceding the measuring operation is used to determine a plurality of arrangement-specific correction parameters of the sensor arrangement, which are stored in a memory unit 14 which is also integrated in the ASIC 10. The memory unit 14 is preferably designed as a non-volatile memory unit, for example as an EEPROM. There are basically various options for performing the calibration. For example, this can be done at the factory during the manufacture of the sensor arrangement or it can only be done later by the respective user. The specific correction parameters determined for each individual sensor arrangement in the calibration mode are used in the Signal processing in the digital signal processing unit 13 is used in measurement mode in order to generate a PWM signal PWM encoding the measured variable with an arrangement-specific duty cycle p. In this way, possible component fluctuations in different sensor arrangements can be taken into account and in this way the correct provision of a measured variable-dependent output signal U _{OUT can be} guaranteed.

In the following, for a further description of the sensor arrangement according to the invention or the measurement and calibration modes provided for operating the same, the determination of the arrangement-specific correction parameters and their use in measuring operation is explained as an example for the measured variable temperature T. In principle, the same procedure can be used for the measured variable humidity rH or any other measured variables.

To carry out the calibration operation or to determine the arrangement-specific correction parameters in the calibration operation, the ASIC 10 of the sensor arrangement according to the invention comprises an interface 16, which is designed, for example, as a known I2C interface. Via the interface 16 and the corresponding signal transmission lines SCL, SCA, the sensor arrangement or the ASIC 10 is connected to a downstream - not in Figure 1 - connected to the control unit, for example via an I2C-USB converter with a PC. It is possible via the interface 16 to cause the output of a PWM signal PWM from the ASIC 10 to the amplifier unit 20, which has a fixed or defined predetermined pulse duty factor p or a fixed predetermined pulse duty factor parameter or PWM value. Specifically, within the scope of the calibration mode, one possible embodiment of the method according to the invention provides for the output of a first PWM signal with the duty cycle parameter or PWM value PWM_FIXL and a second PWM signal with the duty cycle parameter or PWM value PWM_FIXH . In Figure 2a , which shows the second function block 13.2 of the digital signal processing unit 13, the lower switch is used to switch between Measurement and calibration operation indicated. In calibration mode, the pulse duty factor parameters PWM_FIXL, PWM_FIXH are fed to components 13.2a-13.2c to generate corresponding PWM signals PWM, while in measurement mode the pulse duty factor parameter PWM_OUT_NOW with respect to the current measured value is supplied.

In the following, PWM_MAX denotes the value of the maximum pulse duty factor parameter that can be output. A PWM resolution of 16 bits is also assumed in the corresponding sensor arrangement, i.e. the possible duty cycle parameters or PWM values are in the range between 0 and 65,535; the supply voltage VDD for the ASIC 10 is VDD = 3.3V.

bzw. $$\mathrm{PWM}\_\mathrm{OUT}=\left({\mathrm{U}}_{\mathrm{OUT}}-\mathrm{d}\right)/\mathrm{d}$$

mit:

UOUT:=

Wert des analogen Spannungssignals

PWM_OUT :=

Tastverhältnis-Paramater bzw. PWM-Wert des PWM-Signals

k :=

Verstärkungsfaktor der Verstärkereinheit

d :=

Offset der Verstärkereinheit

As in Figure 3 indicated schematically, the amplifier unit 20 converts the respective PWM signal PWM with a defined PWM value PWM_OUT into an analog voltage signal U _OUT according to the following relationship: $${\mathrm{U}}_{\mathrm{OUT}}=\mathrm{k}\cdot \mathrm{PWM}\_\mathrm{OUT}+\mathrm{d}$$

or. $$\mathrm{PWM}\_\mathrm{OUT}=\left({\mathrm{U}}_{\mathrm{OUT}}-\mathrm{d}\right)/\mathrm{d}$$

With:

UOUT: =

Value of the analog voltage signal

PWM_OUT: =

Duty cycle parameter or PWM value of the PWM signal

k: =

Gain factor of the amplifier unit

d: =

Offset of the amplifier unit

In the example, a possible temperature measurement is to be scaled in the range between - 40 ° C and + 60 ° C. This means that the minimum output temperature T_OUT_MIN is T_OUT_MIN = - 40 ° C, the maximum output temperature T_OUT_MAX is T_OUT_MAX = + 60 ° C. The minimum output temperature T_OUT_MIN should have a value OUT_MIN des minimum analog voltage signal U _OUT of OUT_MIN = 0V, the maximum output temperature T_OUT_MAX corresponds to a maximum analog voltage signal U _OUT with OUT_MAX = 10V.

First, in calibration mode, the interface 16 causes the ASIC 10 to output a first PWM signal with a lower, fixed duty cycle parameter value PWM_FIXL = 10,000. For this permanently set PWM value, the value OUT_LOW of the analog output signal U _OUT resulting after the amplifier unit 20 is then measured; this results, for example, at OUT_LOW = 0.573V.

A further, second PWM signal PWM is then output with an upper, fixed duty cycle parameter value PWM_FIXH = 50,000; the analog output signal U _OUT measured for this purpose has the exemplary value OUT_HIGH = 9.573V.

$$\begin{array}{ll}\mathrm{d}& =\mathrm{OUT}\_\mathrm{LOW}-\mathrm{PWM}\_\mathrm{FIXL}\cdot \mathrm{k}\\ & =\mathrm{0,573}-10.000\cdot \mathrm{0,000225}=-\mathrm{1,677}\mathrm{V}\end{array}$$

mit:

• k := Verstärkungsfaktor der Verstärkereinheit
• d := Offset der Verstärkereinheit
• PWM_FIXL := unterer Tastverhältnisparameter-Wert
• PWM_FIXH := oberer Tastverhältnisparameter-Wert
• OUT_MIN := Wert des analogen Ausgangssignals U_OUT bei minimaler Temperatur
• OUT_HIGH := gemessener Wert des Ausgangssignals U_OUT bei oberem Tastverhältnisparameter-Wert PWM_FIXH
• OUT_LOW := gemessener Wert des Ausgangssignals U_OUT bei unterem Tastverhältnisparameter-Wert PWM_FIXL

For the specific sensor arrangement to be calibrated, the parameters k and d from equation 1) and thus the actual relationship between the pulse duty factor p or the associated PWM value PWM_OUT and the output value U _{OUT of} the analog signal U _{OUT can then} be obtained in general as follows (Eq 2a, 2b) or in particular for the example explained: $$\begin{array}{l}k=\frac{\left(\mathit{OUT}\_\mathit{HIGH}-\mathit{OUT}\_\mathit{LOW}\right)}{\left(\mathit{PWM}\_\mathit{FIXH}-\mathit{PWM}\_\mathit{FIXL}\right)}\\ =\frac{\left(\mathrm{9,573}V-0.573V\right)}{\left(\mathrm{50,000}-\mathrm{10,000}\right)}=0.000225\frac{V}{\mathit{LSB}}\end{array}$$

$$\begin{array}{ll}\mathrm{d}& =\mathrm{OUT}\_\mathrm{LOW}-\mathrm{PWM}\_\mathrm{FIXL}\cdot \mathrm{k}\\ & =0.573-\mathrm{10,000}\cdot 0.000225=-1.677\mathrm{V}\end{array}$$

With:

• k: = gain factor of the amplifier unit
• d: = offset of the amplifier unit
• PWM_FIXL: = lower duty cycle parameter value
• PWM_FIXH: = upper duty cycle parameter value
• OUT_MIN: = value of the analog output signal U _OUT at minimum temperature
• OUT_HIGH: = measured value of the output signal U _OUT with the upper pulse duty factor parameter value PWM_FIXH
• OUT_LOW: = measured value of the output signal U _OUT with the lower duty cycle parameter value PWM_FIXL

The amplifier unit 20 must in principle be designed in such a way that an associated PWM value exists in every tolerance case. This means that the PWM value to be output by the ASIC 10 must always be between PWM_OUT = 0 and PWM_OUT = PWM_MAX.

$$\begin{array}{l}\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}=\frac{\mathit{OUT}\_\mathit{MAX}-d}{k}\\ =\frac{\left(\mathrm{10,000}V+\mathrm{1,677}V\right)}{\mathrm{0,000225}}=51.898\end{array}$$

mit:

• PWM_OUT_MIN := erforderlicher PWM-Wert zur Ausgabe von OUT_MIN = 0V im analogen Spannungssignal U_OUT
• PWM_OUT_MAX := erforderlicher PWM-Wert zur Ausgabe von OUT_MAX = 10V im analogen Spannungssignal U_OUT
• k := Verstärkungsfaktor der Verstärkereinheit
• d := Offset der Verstärkereinheit
• OUT_MIN := Wert des analogen Ausgangssignals U_OUT bei minimaler Temperatur
• OUT_MAX := Wert des analogen Ausgangssignals U_OUT bei maximaler Temperatur

This means that the PWM values PWM_OUT_MIN and PWM_OUT_MAX can now be determined individually for the sensor arrangement that has just been calibrated, which are required in order to be able to output exactly the values OUT_MIN = 0V and OUT_MAX = 10V for the analog voltage signal U _OUT via the amplifier unit 20. The corresponding PWM values PWM_OUT_MIN and PWM_OUT_MAX result in general from equation 1b) and for the special example explained here as follows: $$\begin{array}{l}\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}=\frac{\mathit{OUT}\_\mathit{MIN}-d}{k}\\ =\frac{0V+1.667}{0.000225}=\mathrm{7,453}\end{array}$$

$$\begin{array}{l}\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}=\frac{\mathit{OUT}\_\mathit{MAX}-d}{k}\\ =\frac{\left(\mathrm{10,000}V+1.677V\right)}{0.000225}=\mathrm{51,898}\end{array}$$

With:

• PWM_OUT_MIN: = required PWM value to output OUT_MIN = 0V in the analog voltage signal U _OUT
• PWM_OUT_MAX: = required PWM value to output OUT_MAX = 10V in the analog voltage signal U _OUT
• k: = gain factor of the amplifier unit
• d: = offset of the amplifier unit
• OUT_MIN: = value of the analog output signal U _OUT at minimum temperature
• OUT_MAX: = value of the analog output signal U _OUT at maximum temperature

In order to assign a certain pulse duty factor of the PWM signal or a corresponding pulse duty factor parameter or PWM value to a specific measured value of the measured variable T, an arrangement-specific assignment rule is stored in the digital signal processing unit 13. In the form of a linear interpolation, this describes a linear relationship between the respective current measured value MV_NOW of the sensor signal T_ASIC and the associated duty cycle parameter PWM_OUT_NOW. The corresponding relationships are highly schematized in the Figures 2a and 2 B shown, where Figure 2a the second function block 13.2 of the digital signal processing unit 13 and Figure 2b shows a detailed representation of the linear interpolation taking place.

Using the specifically explained example for temperature measurement, the following is the linear interpolation with the aid of Figure 2b explained.

$$\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}=6.000\left(=\mathrm{T}\_\mathrm{OUT}\_\mathrm{MAX}*100\right)$$

The values MV_OUT_MIN and MV_OUT_MAX entered along the y-axis represent the lower and upper limit values of the temperature T to be output in steps of 1/100 ° C. The following therefore applies to this example: $$\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}=-\mathrm{4,000}\left(=\mathrm{T}\_\mathrm{OUT}\_\mathrm{MIN}*100\right)$$

$$\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}=\mathrm{6,000}\left(=\mathrm{T}\_\mathrm{OUT}\_\mathrm{MAX}*100\right)$$

_{This means that the minimum voltage OUT_MIN = 0V is output for the analog voltage signal U OUT} at the minimum temperature T_OUT_MIN = - 40 ° C and the maximum voltage OUT_MAX = 10,000V is output at the maximum temperature T_OUT_MAX = 60 ° C.

The variables PWM_OUT_MIN and PWM_OUT_MAX, i.e. the minimum and the maximum duty cycle parameter limit value, thus represent arrangement-specific correction parameters that are stored in a memory unit 14 in the ASIC 10 at the factory or by the customer after the calibration operation has been carried out for the respective sensor arrangement. They are used during the measurement operation in order to correct possible component fluctuations and remain permanently stored in the preferably non-volatile memory unit 14 over the life of the sensor arrangement.

In addition to the arrangement-specific correction parameters PWM_OUT_MIN, PWM_OUT_MAX, the variables MV_OUT_MIN, MV_OUT_MAX, i.e. the lower and upper sensor limit measured values of the temperature T to be output, which limit the desired measuring range, can also be stored in the memory unit 14. If necessary, this can also be suitably changed later by changing the corresponding measured sensor limit values and adapted to the respective measurement requirements.

mit:

• PWM_OUT_NOW := Tastverhältnisparameter des PWM-Signals
• MV_NOW := Messwert des Sensors
• $k_{\mathit{PWM}}:=\frac{\left({\mathit{PWM}}_{{\mathit{OUT}}_{\mathit{MAX}}}-{\mathit{PWM}}_{{\mathit{OUT}}_{\mathit{MIN}}}\right)}{\left({\mathrm{MV}}_{{\mathrm{OUT}}_{\mathrm{MAX}}}-{\mathrm{MV}}_{{\mathrm{OUT}}_{\mathrm{MIN}}}\right)}$
  
• d_PWM = PWM_OUT_MIN - MV_OUT_MIN ^∗ k_PWM

The corresponding pulse duty factor parameter or PWM value results for a currently recorded measured value MV_NOW of the respective sensor PWM_OUT_NOW of the associated PWM signal then by linear interpolation between the two limit values PWM_OUT_MIN, PWM_OUT_MAX along the solid line in Figure 2b . This linear interpolation is stored in the digital signal processing unit 13 as an arrangement-specific conversion rule. It applies here $$\mathrm{PWM}\_\mathrm{OUT}\_\mathrm{NOW}={\mathrm{k}}_{\mathrm{PWM}}\cdot \mathrm{MV}\_\mathrm{OUT}\_\mathrm{NOW}+{\mathrm{d}}_{\mathrm{PWM}}$$

With:

• PWM_OUT_NOW: = duty cycle parameter of the PWM signal
• MV_NOW: = measured value of the sensor
• $k_{\mathit{PWM}}:=\frac{\left({\mathit{PWM}}_{{\mathit{OUT}}_{\mathit{MAX}}}-{\mathit{PWM}}_{{\mathit{OUT}}_{\mathit{MIN}}}\right)}{\left({\mathrm{MV}}_{{\mathrm{OUT}}_{\mathrm{MAX}}}-{\mathrm{MV}}_{{\mathrm{OUT}}_{\mathrm{MIN}}}\right)}$
  
• d _PWM = PWM_OUT_MIN - MV_OUT_MIN ^∗ k _PWM

$$d_{\mathit{PWM}}=7453+4.000\ast \mathrm{4,444444}=25.230,78\cong 25.231$$

In the concrete example, the following results for the two variables k _PWM and d _PWM with the values given above: $$k_{\mathit{PWM}}=\frac{\left(\mathrm{51,898}-7453\right)}{\left(\mathrm{6,000}+\mathrm{4,000}\right)}=4.4444$$

$$d_{\mathit{PWM}}=7453+\mathrm{4,000}\ast \mathrm{4,444444}=\mathrm{25,230},78\cong \mathrm{25,231}$$

$$\begin{array}{l}\mathit{PWM}\_\mathit{OUT}\_\mathit{NOW}=\mathit{MV}\_\mathit{NOW}\ast k_{\mathit{PWM}}+d_{\mathit{PWM}}=2.500\ast \mathrm{4,4444}+25.231\\ =36.342,25\cong 36.342\end{array}$$

For example, if there is a current measured temperature value of 25.00 ° C, the associated PWM value PWM_OUT_NOW of the PWM signal PWM to be generated in function block 13.2 can be determined as follows: $$\mathit{MV}\_\mathit{NOW}=T\_\mathit{ACT}\ast 100=25.00\ast 100=\mathrm{2,500}$$

$$\begin{array}{l}\mathit{PWM}\_\mathit{OUT}\_\mathit{NOW}=\mathit{MV}\_\mathit{NOW}\ast k_{\mathit{PWM}}+d_{\mathit{PWM}}=\mathrm{2,500}\ast 4.4444+\mathrm{25,231}\\ =\mathrm{36,342},\mathrm{25th}\cong \mathrm{36,342}\end{array}$$

In the case of a PWM value PWM_OUT_NOW = 36.342 selected in this way, equation 1a) ensures that the analog voltage signal U _OUT has exactly the value 6.49995V on the output side. The difference to 6.5000V results from the discretization of the value for PWM_OUT_NOW from a real number to a 16-bit number.

After the required PWM value PWM_OUT_NOW has been determined via the linear interpolation carried out in the second function block 13.2 of the digital signal processing unit 13, this value can then then be used via the PWM comparator stage 13.2c, the PWM clock generation unit 13.2a and the PWM counter unit 13.2b Square-wave signal PWM are generated and transferred to the amplifier unit 20. In this case, the PWM counter unit 13.2b is fed with a clock signal from the PWM clock generation unit 13.2a and, for example, counts up with each rising clock signal edge. As long as the count is up, the PWM comparator stage 13.2a outputs a HIGH signal (VDD) at the output. If the value PWM_OUT is reached, the PWM comparator stage 13.2a switches the output signal from HIGH (VDD) to LOW (0V). In the event of a counter overflow, e.g. when changing from counter value 65,535 to 0, a HIGH signal (VDD) is output at the output of PWM comparator stage 13.2a.

In this way, depending on the existing component tolerances, an arrangement-specific PWM value PWM_OUT_NOW is set for a specific measured value MV_NOW. This means that for a certain, calibrated sensor arrangement, an arrangement-specific relationship is specified between the measured value to be output and the PWM value, which is used to generate the analog output signal U _OUT in the measuring mode. Due to the arrangement-specific correction parameters PWM_OUT_MIN, PWM_OUT_MAX permanently stored in the memory unit 14, this can be taken into account over the entire service life of the respective sensor arrangement. The entire sensor arrangement consisting of ASIC 10 and amplifier unit 20 can thus be controlled by means of the measures according to the invention Reliably adjust or compensate for any component fluctuations in the ASIC 10 as well as in the amplifier unit 20. For calibration, it is not necessary here to expose the sensor arrangement to a changed temperature; that is, the calibration operation can be carried out without changing the temperature of the sensor arrangement.

In addition to the exemplary embodiments described above, there are of course still further design options within the scope of the present invention.

In this way, for example, a sensor arrangement can also be constructed according to the invention in which an analog current signal is generated from the PWM signal on the output side via the amplifier unit, etc.

Claims (13)

1. Sensor arrangement, having

   - at least one sensor (11, 12) that records changeable physical measured variables (T, rH) and provides a sensor raw signal (T_RAW, rH_RAW) at output,

   - a digital signal processing unit (13; 13.1, 13.2) for preprocessing the sensor raw signal (T_RAW, rH_RAW) provided by the sensor (11, 12) into a sensor signal (T_ASIC, rH_ASIC), for further processing the sensor signal (T_ASIC, rH_ASIC) into a pulse width-modulated output signal (PWM) having a duty cycle (p) dependent on the measured variable (T, rH), for which purpose a plurality of arrangement-specific correction parameters (PWM_OUT_MIN, PWM_OUT_MAX) are stored in a memory unit (14) and are used by the signal processing unit (13; 13.1, 13.2) to convert the sensor signal (T_ASIC, rH_ASIC) into the pulse width-modulated output signal (PWM), wherein at least a minimum duty cycle parameter limit value and a maximum duty cycle parameter limit value are stored in the memory unit (14) as arrangement-specific correction parameters (PWM_OUT_MIN, PWM_OUT_MAX), and

   - an amplifier unit (20) that converts the pulse width-modulated output signal (PWM) into an analogue voltage or current signal (U_out)
2. Sensor arrangement according to Claim 1, wherein an arrangement-specific conversion rule is stored in the digital signal processing unit (13; 13.1, 13.2) and describes a linear relationship between the measured value (MV_NOW) of the sensor signal (T_ASIC, rH_ASIC) and a duty cycle parameter (PWM_OUT_NOW) of the pulse width-modulated output signal (PWM).
3. Sensor arrangement according to Claim 1, wherein the memory unit (14) furthermore stores a minimum sensor limit measured value (MV_OUT_MIN) and a maximum sensor limit measured value (MV_OUT_MAX) that define the sensor measurement range.
4. Sensor arrangement according to at least one of Claims 1 - 3, wherein the relationship $$\mathrm{PWM}\_\mathrm{OUT}\_\mathrm{NOW}=\mathrm{MV}\_\mathrm{NOW}\cdot {\mathrm{k}}_{\mathrm{PWM}}+{\mathrm{d}}_{\mathrm{PWM}}$$

   

   is stored in the digital signal processing unit (13; 13.1, 13.2) as arrangement-specific conversion rule, where

   PWM_OUT_NOW:= duty cycle parameter of the PWM signal

   MV_NOW:= measured value from the sensor ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$

   

   d_PWM := PWM_OUT_MIN - MV_OUT_MIN · k_PWM

   PWM_OUT_MAX:= maximum duty cycle parameter limit value

   PWM_OUT_MIN:= minimum duty cycle parameter limit value

   MV_OUT_MAX:= maximum sensor limit measured value

   MV_OUT_MIN:= minimum sensor limit measured value.
5. Sensor arrangement according to at least one of the preceding claims, wherein the at least one sensor (11, 12), the digital signal processing unit (13; 13.1, 13.2) and the memory unit (14) are arranged together in an ASIC (10) and the amplifier unit (20) is formed separately from the ASIC (10).
6. Sensor arrangement according to Claim 5, wherein the memory unit (14) is designed as a non-volatile memory unit.
7. Sensor arrangement according to at least one of the preceding claims, wherein the amplifier unit (20) is designed as an amplifier circuit with a low-pass filter.
8. Sensor arrangement according to at least one of the preceding claims, having two sensors (11, 12), a first sensor (11) of which is designed as a temperature sensor and a second sensor (12) of which is designed as a moisture sensor.
9. Method for operating a sensor arrangement in a measurement mode and in a calibration mode, wherein

   - in the measurement mode

   - at least one sensor (11, 12) records a changeable physical measured variable (T, rH) and provides a sensor raw signal (T_RAW, rH_RAW) at output, and

   - a digital signal processing unit (13; 13.1, 13.2) preprocesses the sensor raw signal (T_RAW, rH_RAW) provided by the sensor (11, 12) into a sensor signal (T_ASIC, rH_ASIC) and converts the sensor signal (T_ASIC, rH_ASIC) into a pulse width-modulated output signal (PWM) having a duty cycle dependent on the measured variable (T, rH), and

   - an amplifier unit (20) converts the pulse width-modulated output signal (PWM) into an analogue voltage or current signal (U_out), and

   - in a calibration mode preceding the measurement mode, a plurality of arrangement-specific correction parameters (PWM_OUT_MIN, PWM_OUT_MAX) are stored in a memory unit (14) and are used by the signal processing unit (13; 13.1, 13.2), in the measurement mode, to convert the sensor signal (T_ASIC, rH_ASIC) into the pulse width-modulated output signal (PWM), wherein at least a minimum duty cycle parameter limit value and a maximum duty cycle parameter limit value are stored in the memory unit (14) as arrangement-specific correction parameters (PWM_OUT_MIN, PWM_OUT_MAX).
10. Method according to Claim 9, wherein, in the calibration mode, an arrangement-specific conversion rule is stored in the digital signal processing unit (13; 13.1, 13.2) and describes a linear relationship between the measured value (MV_NOW) of the sensor signal (T_ASIC, rH_ASIC) and a duty cycle parameter (PWM_OUT_NOW) of the pulse width-modulated output signal (PWM).
11. Method according to Claim 9, wherein the memory unit (14) furthermore stores a minimum sensor limit measured value (MV_OUT_MIN) and a maximum sensor limit measured value (MV_OUT_MAX) that define the sensor measurement range.
12. Method according to Claims 9 - 11, wherein the relationship $$\mathrm{PWM}\_\mathrm{OUT}\_\mathrm{NOW}=\mathrm{MV}\_\mathrm{NOW}\cdot {\mathrm{k}}_{\mathrm{PWM}}+{\mathrm{d}}_{\mathrm{PWM}}$$

    

    is stored in the digital signal processing unit (13; 13.1, 13.2) as arrangement-specific conversion rule, where

    PWM_OUT_NOW:= duty cycle parameter of the PWM signal

    MV_NOW:= measured value of the sensor signal ${\mathrm{k}}_{\mathrm{PWM}}:=\frac{\left(\mathit{PWM}\_\mathit{OUT}\_\mathit{MAX}-\mathit{PWM}\_\mathit{OUT}\_\mathit{MIN}\right)}{\left(\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MAX}-\mathrm{MV}\_\mathrm{OUT}\_\mathrm{MIN}\right)}$

    

    d_PWM:= PWM_OUT_MIN - MV_OUT_MIN · k_PWM

    PWM_OUT_MAX:= maximum duty cycle parameter limit value

    PWM_OUT_MIN:= minimum duty cycle parameter limit value

    MV_OUT_MAX:= maximum sensor limit measured value

    MV_OUT_MIN:= minimum sensor limit measured value.
13. Method according to at least one of Claims 9 - 12, wherein the calibration mode is performed without changing the temperature of the sensor arrangement.

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